Air–water gas exchange of α-hexachlorocyclohexane enantiomers in the South Atlantic Ocean and Antarctica

Between November 1997 and February 1998, air and water samples were collected on the African side of the South Atlantic Ocean to Antarctica, on board the S.A. Agulhas, to determine the spatial distribution of α-hexachlorocyclohexane (α-HCH) and the net direction of air/water gas exchange. The α-HCH concentrations in air and surface water were much lower than in Arctic regions, consistent with the historically lower usage of technical HCH in the Southern Hemisphere. The water/air fugacity ratios of α-HCH were ⩽1.0, indicating steady state or net deposition conditions. The α-HCH in water was enantioselectively metabolized, with resulting enantiomer fractions (EFs) that differed from the racemic (0.500) value of the technical product. The EFs decreased from >0.500 at the lower latitudes to <0.500 farther south, indicating preferential loss of (−)α-HCH or (+)α-HCH in different ocean regions. EFs in the air boundary layer reflected those in surface water, showing the bidirectional nature of gas exchange.